This invention relates to particles, which are capable of generating signal, for use in methods, compositions and kits for determining an analyte in a sample. The invention further relates to the stabilization of signal generated by such particles.
The clinical diagnostic field has seen a broad expansion in recent years, both as to the variety of materials of interest that may be readily and accurately determined, as well as the methods for the determination. Most methods involve generation of a signal in relation to the presence and/or amount of one or more analytes in a sample. Luminescent compounds, such as fluorescent compounds and chemiluminescent compounds, find wide application in the assay field because of their ability to emit light. Particles, such as latex particles, liposomes and the like have been utilized in assays. Dyed latex particles have been used previously not only in immunoassays but also for other diverse uses such as photodynamic therapy and as pigments. Both absorptive dyes and dyes that impart fluorescent or chemiluminescent properties have been incorporated into particles. In one particular approach, particles that comprise one or more metal chelates such as, for example, lanthanide chelates, are employed for generating a signal.
An induced luminescence immunoassay is described in U.S. Pat. Nos. 5,340,716 and 6,251,581, which disclosures are incorporated herein by reference. In one approach the assay uses a particle incorporating a photosensitizer and a label particle incorporating a chemiluminescent compound. The label particle is conjugated to a specific binding pair (sbp) member that is capable of binding to an analyte to form a complex, or to a second sbp member to form a complex, in relation to the presence of the analyte. If the analyte is present, the photosensitizer and the chemiluminescent compound come into close proximity. The photosensitizer generates singlet oxygen and activates the chemiluminescent compound when the two labels are in close proximity. The activated chemiluminescent compound subsequently produces light. The amount of light produced is related to the amount of the complex formed, which in turn is related to the amount of analyte present. In one particular approach, the chemiluminescent particles comprise one or more metal chelates such as, for example, lanthanide chelates.
In a variation of the induced luminescence method, a particulate support is employed that comprises both (a) a photosensitizer capable upon irradiation of generating singlet oxygen and (b) a chemiluminescent compound capable of being activated by singlet oxygen. The methods allow for generating delayed luminescence, which can be realized upon irradiation of the support. The methods have application to the determination of an analyte in a medium suspected of containing the analyte. One method comprises subjecting a medium suspected of containing an analyte to conditions under which a complex of sbp members is formed in relation to the presence of the analyte and determining whether the sbp member complex has formed by employing as a label a particulate composition having both chemiluminescent and photosensitizer properties. Upon activation of the photosensitizer property singlet oxygen is generated and activates the chemiluminescent property. Such compositions and methods are described in U.S. Pat. No. 5,709,994, the relevant disclosure of which is incorporated herein by reference.
There is a continuing need to maximize signal generation in label reagents for use in assays. Signal response to changes in the concentration of analyte is an important consideration in assay development. Such label reagents should provide for maximized performance including sensitivity.